Multi-stove blast furnace installation with staggered operation of stoves



April 13, 1965 L. WALTHER ETAL MULTI-STOVE BLAST FURNACE INSTALLATION WITH STAGGERED OPERATION OF STOVES 4 Sheets-Sheet 1 Filed Aug. 27, 1962 wmmw S @www E@ sin k RSS @s April 13, 1,965 L. WALTHER ETAL MULTI-STOVE BLAST FURNACE INSTALLATION WITH STAGGERED OPERATION OF STOVES 4 Sheets-Sheet 2 Filed Aug. 27, 1962 w N Q Aprxl 13, 1965 L.. wALTHl-:R ETAL 3,178,160

MULTI-STOVE BLAST FURNACE INSTALLATION WITH STAGGERED OPERATION OF STOVES Filed Aug. 27, 1962 4 Sheets-Sheet 3 nl nl N April 13, 1965 MULTI-STOVE BLAST FURNACE INSTALLATION WITH Filed Aug. 27, 1962 L. WALTHER ETAL 3,178,160

STAGGERED OPERATION OF STOVES 4 vSheets-Sheet 4 Arran/V575' United States Patent O MULTl-STOVE BLAST FURNACE INSTALLATON WTH STAGGERED OPERA'I'ION 0F STOVES Ludwig Walther, Buren, Rhineland, Germany, and

George Schaffer, Pittsburgh, Pa., assignors to Zimmermann & Jansen G.m.b.H., Duren, Rhineland, Germany,

a corporation of Germany Filed Aug. 27, 1962, Ser. No. 219,453 7 Claims. (Cl. 263-19) The present invention relates to the operation and control of a plurality of hot blast stoves which are adapted to supply a continuous stream of hot blast to a blast furnace.

In the operation of a blast furnace it is desirable to supply a continuous stream of hot blast to the blast furnace. Such hot blast is supplied to the blast furnace by rst heating the checker Work of a hot blast stove and thereafter passing cold air, commonly known as cold blast through such heated stove, whereby the cold blast becomes hot blast to be introduced into the furnace. When a stove is being heated it is commonly referred to as being ON GAS, and when such heated stove has air passed therethrough it is commonly referred to as being ON BLAST.

In order to maintain a continuous supply of hot blast entering into the blast furnace, it is necessary to have a plurality of hot lblast stoves so that While one of these stoves is ON BLAST the other stove or stoves are ON GAS so as to be ready to go into the ON BLAST condition when a freshly heated stove is required. In addition to supplying a continuous stream of hot blast to the blast furnace it is further desirable that such continuous stream of hot blast be maintained at a relatively constant predetermined set temperature depending on the particular requirements of the blast furnace. When a stove `is initially placed in the ON BLAST condition, its checker work is the hottest, and the hot blast exiting from such stove is obviously at the highest temperature of the ON BLAST cycle. As the stove which is ON BLAST continues to supply hot blast, its checker work will gradually cool down so that the exiting hot blast from such stove has a gradually decreasing temperature. In order, however, to maintain the temperature of the hot blast entering into the blast furnace relatively constant, it is customary to combine the hot blast exiting from the stove with cold blast in order to provide the required resultant blast temperature. Accordingly, -at the beginning of a stoves ON BLAST cycle7 when the exiting hot blast therefrom has the highest temperature, a relatively large amount of cold blast is required to be combined with such exiting hot blast in order to obtain the desired resultant hot blast temperature. As the stove which is ON BLAST continues to supply hot blast, its temperature gradually decreases, thereby requiring a smaller amount of cold blast to be combined therewith. The amount of cold blast to be combined with the exiting hot blast from the stove keeps on decreasing until the point is reached where the temperature of the exiting hot blast from the stove reaches the desired resultant temperature and, at such time, it becomes necessary to introduce a freshly heated stove into the system. A multi-stove installation for automatically providing a continuous stream of hot blast to a blast furnace in the manner described above is set forth in United States Patent No. 3,034,775, assigned to the assignee hereof.

The one predominant feature of the prior art system described above is that there is only one stove at a time which supplies the requisite hot blast to the furnace, the other stove or stoves being, at such time, in a condition different from the ON BLAST condition such as, for

3,178,166 Patented Apr. 13, 1965 example, the ON GAS condition during which they are being heated.

In accordance with the present invention the hot blast adapted to be supplied to the blast furnace is provided simultaneously by two stoves instead of by just one stove, as in the prior art. More specically, in accordance with the present invention, the hot blast entering the blast furnace is constituted by combining the exiting hot blast of two different stoves which, while they are both in the ON BLAST condition, are not providing hot blast at the same temperature. The two stoves which are ON BLAST are in staggered relation and one of these provides hot blast at a relatively higher temperature than the other. In order to provide the requisite resultant temperature, there is provided means for automatically adjusting the relative volume of cold blast passed through the two stoves, making it unnecessary to utilize cold blast for the purpose of controlling the temperature of the blast entering the blast furnace, and resulting in a system which operates at a much greater efliciency. Furthermore, the utilization of more than one stove at any one time for the purpose of supplying hot blast to the blast furnace provides better continuity of supply of hot blast to the furnace at a constant temperature.

By utilizing the staggered arrangement of the present invention the capacity of an installation can be greatly increased, though retaining the use of the same stoves as are presently existing in said installation.

It is therefore an object of the present invention to provide a multi-stove installation for a blast furnace in which the stoves are placed in the ON BLAST condition in staggered relation and in which, during the operation of the system, the hot blast supplied to the blast furnace is obtained from more than one stove.

Another object of the present invention is to provide in a blast furnace installation in which more than one stove supplies hot blast to the blast furnace at any one time, means for automatically controlling the respective volurnes of blast passing through the stoves which are supplying hot blast, in order to obtain a predetermined resultant blast temperature.

Another object is the provision, in a blast furnace installation in which two stoves, in staggered relation, are ON BLAS at the same time, of means for maintaining the resultant temperature of said two stoves relatively constant and equal to a predetermined set temperature.

Another object is the provision, in a blast furnace installation in which two stoves, in staggered relation, are ON BLAST at the same time, of means for maintaining the resultant temperature of the blast of said two stoves relatively constant and equal to a predetermined set temperature, by cont-rolling the proportioning valve of only one of said two stoves while the proportioning valve of the other stove remains in a fixed open condition.

Another object is the provision, in a blast furnace installation in which two stoves, in staggered relation, are ON BLAST at the same time, of means for automatically controlling the proportioning valve of one of said stoves while retaining the proportioning valve of the other stove in fixed open condition, for maintaining the resul*- ant temperature of the combined blast of said two stoves relatively constant and equal to a predetermined set temperature.

The above and other objects, features and advantages of the present invention will be more fully understood from the following description considered in connection with the accompanying illustrated drawings.

In the drawings:

FIG. 1 is a schematic layout of a blast furnace installation showing the utilization of four hot blast stoves, in accordance with the invention;

FIG. 2 is a graph showing the relationship between the temperature of the hot blast and time, for each of the respective stoves, in accordance with the invention;

FIG. 3 is a composite graph showing the manner in which the proportioning valves for the respective stoves are operated, with respect to time, in accordance with the invention;

FIG. 4 is a schematic circuit diagram of the circuitry associated with the four stoves, for automatically selecting the particular stove to be controlled, in accordance with the invention;

FIG. 5 is a schematic diagram of the circuitry associated with the four stoves for automatically determining the manner in which the stove selected by the circuitry of FIG. 4 is controlled in accordance with the invention; and

FIG. 6 is a schematic layout similar to FIG. 1, but slightly modified in accordance withanother embodiment orr the invention.

Referring now to the drawings, and particularly to FIG. 1, there is shown a blast furnace installation provided with four hot blast stoves identified by Roman numerals I, II, III and IV, respectively. Stove I is provided with a cold blast valve CBV-I which functions to isolate stove I from the cold blast main. Between cold blast valve CEV-I and stove I proper there is provided a proportioning valve PV-I. At the opposite side of stove I there is provided a hot blast valve HBV-I which isolates stove I from the hot blast main, the latter leading into the blast furnace. When a stove such as stove I is placed in the ON BLAST condition all of its valves are operated in a particular sequence which includes the complete opening of cold blast valve CBV-I and hot blast valve HBV-I, respectively. An apparatus for the Vautomatic sequential operation of the valves of a stove to place the latter in any one of a plurality of operating conditions such as ON BLAST or ON GAS is shown and described in United States Patent No. 2,931,635, assigned -to the assignee hereof.

Proportioning valve PV-I is operated by valve control drive VCD-I, the latter having a pair of input terminals o and c, respectively. When VCD-I is energized through terminal o, it will cause proportioning valve PV-I to move in an opening direction. Conversely, when VCD-I is energized through terminal c, it will cause PV-I-to move in a closing direction. It will be understood that the extent to which PV-I is opened will determine the amount ofA cold blast permitted to enter stove I to be heated lby the latter.

Similarly to stove I, each of stoves II, III and IV is provided with a cold blast valve, CBV, a proportioning valve PV, a control drive VCD and a hot blast valve HBV. In this connection it will be understood that the Roman numerals I, II, III and IV which identify the respective stoves are also used to identify the various valves, elements, components, etc; associated with stove I, stove II, stove III and stove IV, respectively.

In accordance with the preferred embodiment of the present invention, the hot blast supply to the blast furnace is provided by two hot blast stoves at one time. For purposes of explanation, let us assume that stove I and stove II are the ones which are presently supplying the requisite hot blast to the blast furnace. Let us further assumethat stove I has been ON BLAST for some time and stove II has just been placed in the ON BLAST condition. Under these circumstances, since `stove II is the freshest of the stoves, the temperature of the hot blast exiting from stove II is far greater than the temperature of the hot blast exiting from stove I.

The above conditions are best illustrated by reference to FIG. 2 which shows a graph of temperature of exiting hot blast for the `particular stoves vs. time. At time a, which is the moment that stove II is placed in the ON BLAST condition, the temperature of the exiting hot blast from stove II is shown to be at a maximum. At

I and II at point a.

the same time the temperature of the exiting hot blast from stove I is shown to be at a substantially lower temperature since stove I has been ON BLAST for some time. FIG.,2 also shows a constant temperature horizontal line identified by reference character ST, such ternperature being the set temperature `for the blast furnace or, in other words, the predetermined desired temperature of the hot blast entering the blast furnace. Obviously, it is at point a, when the temperature of the hot blast exiting from stove I reaches the set temperature ST that it became necessary for a fresh stove, namely stove II to be placed into the system so that it is possible to combine the output of stove I with the output of stove II from point a on, in particular proportions, in lorder to maintain the resultant temperature of the blast at the set temperature ST. What is apparent from FIG. 2 is that with the passage of time the temperature of the exiting hot blast of stoves I and II will gradually decrease. Referring again to point a in FIG. 2, it will be apparent that at such point, in order to have a resultant temperature equal to the set temperature ST, the entire blast to be supplied to the blast furnace must come from stove I which is then, as previously stated, at the temperature ST. As time passes, however, and stove I cools down, such as for example at the point x, it will be necessary, in order to maintain the .resultant temperature of ST, to have a large amount of blast coming from stove I and a relatively smaller amount of blast from stove II. At point a on FIG. 2, the temperature relationship between stoves I and II (the temperature of stove II exceeds ST by approximately the same extent as ST exceeds the temperature of stove I), is such that it will be necessary, in order to maintain the resultant temperature at ST, to have approximately equal amounts of blast-coming from stove ,I and stove II. From point a' on, itis stove II which must supply increasingly larger amounts of blast while stove I supplies decreasing amounts of blast in order to maintain the resultant temperature at ST. This continues until stove II reaches the ST temperature (point b), at which time it becomes neccssary to place a fresh stove, such as stove III, into the ON BLAST condition. At the same time, of course, stove I is no longer `useful and is taken olf the ON BLAST condition and placed into the ON GAS condition so that it can be reheated and be available again at some later time. At Vpoint b, it will be noted, stoves II and III are in the same relative condition as were stoves At point c in FIG. 2, stove III has cooled down to the desired temperature ST and it becomes necessary to put a fresh stove, namely stove 1V, in the ON BLAST condition. At point d, stove IV has cooled down to the desired temperature ST and it becomes necessary to place stove I into the ON BLAST condition. At point e in FIG. 2, stove I has cooled down to the set temperature ST and it becomes necessary to place a fresh stove into the ON BLAST condition, such as stove II. Point e, it will be noted, is identical to point a, and from then on the cycle is repeated in exactly the same way as shown beginning with point a.

FIG. 2 thus demonstrates the staggered arrangement of the stoves whereby two stoves are always in the ON BLAST condition and their outputs are combined in order to produce the desired resultant temperature. The primary problem confronted by staggering the stoves in the arrangement shown in FIG. 2 is that of properly proportioningthe amount of blast volume to be supplied by each of the two stoves which are in the ON BLAST condition. In this connection it must also be remembered that in addition to providing hot blast to the blast furnace at a uniform, predetermined desired temperature, it is also necessary to maintain a relatively constant volume of blast entering into the blast furnace. Accordingly, at any one moment, no matter what relative amounts are required between the two stoves which are ON BLAST in order to provide the relative set temperature ST, it is also necessary that the sum of the blast volumes going through the two stoves be constant.

In accordance with the invention, the amount of blast volume delivered to the blast furnace is determined by the total volume of cold blast which is permitted t enter the cold blast main. Any suitable conventional means may be utilized to supply a constant volume of air in the cold blast main. The manner in which this cold blast volume is distributed between the stoves which are in the ON BLAST condition is, in accordance with e invention, determined by the relative position of the proportioningr valves PV of the two stoves. If, for example, with stove I and stove II in the ON BLAST condition, the proportioning valve PV-H were to be fully closed, then all of the blast volume would pass through stove I, so long as PV-I was opened, no matter what the extent of such opening would be. Let us assume, for purposes of illustration that PV-I is fully opened and PV-II is fully closed. Under such circumstances, the entire blast volume would pass through stove I. If PV-II is now opened slightly while PV-I remains fully open, some of the blast will pass through stove II, the amount of which would be a function of the extent to which PV-H is opened. Thus it is noted that though one stove may have its proportioning valve fully opened, the amount of blast passing through such stove may be reduced when the proportioning valve of the companion stove is increasingly opened. In other words, by keeping one of the two proportioning valves fully opened it is possible to control the amount of blast volume passing through both stoves by merely controlling the extent of opening of the proportioning valve of the other stove. It is this principle which is utilized in the present invention for automatically controlling the relative volumes of blast through the stoves which are ON BLAST in order t0 continuously maintain a resultant blast temperature equal to the set ternperature ST.

The above is clearly illustrated with reference to FIG. 3 which is a composite graph showing the condition of the proportioning valve of each stove with respect to time, the time axis in FIG. 3 being identical to the time axis in FIG. 2. It will be recalled that at time a in FIG. 2 the temperature of stove I was exactly that of the set temperature ST while the temperature of stove II was the maximum, since stove II, at point a, is at the Very beginning of its ON BLAST cycle. At this point a as has been previously stated, all of the blast volume to be supplied to the blast furnace comes from stove I which is at the set temperature ST and no blast volume cornes from stove II. This condition is illustrated in FIG. 3 at point a where the proportioning valve of stove I is shown as being fully opened while the proportion valve of stove II is shown as being fully closed. At point x stove I is just slightly below the set temperature ST while the temperature of stove II is substantially higher. At such point, in order to obtain a resultant temperature equal to ST the bulk of the blast is supplied fromk stove I while only a minor fraction of the blast is supplied by stove Il. This is accomplished by maintaining the proportioning valve PV-I of stove I fully opened and by opening very slightly the proportioning valve of stove II, as shown in FIG. 3. As time passes, more and more blast is to be supplied by stove II and a correspondingly lesser amount is to be supplied by stove I. This, as shown in FIG. 3, is accomplished by merely gradually opening the proportioning valve of Astove II while leaving the proportioning valve of stove I fully opened. The gradually increasing opening of PV-II continues until point a is reached, at which time the temperature relationship between stove I and stove .II is such that resultant temperature ST is maintained by having PV-II and PV-I in fully open position. This is shown in FIG. 3 by the fact that at the point a the proportioning valve of stove II has reached its fully open position. Thus it is seen that between points a and a' the distribution of blast between stoves I and II, in order to maintain a constant resultant temperature ST, has been obtained by controlling the proportioning valve of only one of the two stoves, namely that of stove II.

From point a on, it will be necessary to provide a greater proportion of blast volume through stove II than through stove I in order to maintain the resultant temperature at the desired value ST. This is done, as shown in FIG. 3, by maintaining, beginning with point a', the proportioning valve of stove II in fully open condition while gradually closing the proportioning valve of stove I. This continues until point b is reached, such being the point at which stove II has reached a temperature equal to the set temperature ST. At this point, as has previously been described, it is necessary to bring a new stove into the ON BLAST condition, namely stove III. In order to maintain the resultant temperature constant at ST, the proportioning valve of stove II remains fully open at point b while the proportioning valve of stove III gradually opens until it reaches its fully open position at point b', which is the point at which the ternperature of stove III exceeds the set temperature ST by the same amount that STY exceeds the temperature of stove II. From point b on, the proportioning valve of stove III remains fully opened while the proportioning valve of stove II gradually closes until it reaches point c. The cycle is repeated with respect to the other stoves as clearly shown in FIG. 3. The important observation to be made from FIG. 3 is that at all times only one of the two proportioning valves of the stoves which are ON BLAST is being controlled, the other proportioning valve being in a fixed fully open position. This permits the automatic control device, to be described hereinafter, to operate on only one valve at any one time, such automatic control-shifting from one stove to another from time to time as indicated by FIG. 3 and as will hereinafter be more fully described.

In describing FIG. 2 above, reference has been made .to the fact that at point b it is time for a fresh stove to be placed in the ON BLAST condition, such fresh stove being stove III. At such point b, stove I is also taken olf the ON BLAST condition and placed into the ON GAS condition, so that it may be reheated and be ready for future use in the ON BLAST condition. The change over of stoves I and III from one condition toanother, as just described, is accomplished in a fully automatic manner, and such automatic change over is fully described and illustrated in previously referred to Patent No. 3,034,775, assigned to the assignee hereof. More specifically, in accordance with the invention of Patent No. 3,034,775, there is provided a system for automatically placing a new stove in the ON BLAST condition when the need for it arises and to automatically place the stove which has completed its ON BLAST cycle into the ON GAS condition. While this automatic changeover feature is utilized in the present invention, it does not form part of the present invention, which relates primarily to the control of the stoves which are ON BLAST in a staggered relation, in order to maintain the temperature of the combined blast exiting from the stoves at a constant predetermined temperature.

In accordance with the present invention the staggered operation of the multi-stove installation described above is continuously operated in a fully automatic manner. The automatic system performs the following functions. At time a (FIGS. 2 and 3), while the proportioning valve of stove I is fully opened, proportioning valve of stove IVI, namely PV-II is automatically controlled beginning with its fully closed position. More specifically, propor- Vtioning valve PV-II will be gradually controlled in order to maintain the resultant temperature of the blasts coming out of stoves I and II constant. In other words, in

accordance with the automatic control system, PV-II will be gradually opened beginning with point a so as to automatically maintain the resultant temperature constant and equal to a predetermined set temperature. If, however, at any time between points a and a', the resultant temperature should exceed the desired set temperature ST, the automatic control system is operative to close proportioning valve PV-II until the resultant temperature returns to the desired set temperature ST. Some hunting 'therefore does take place between points a and a in order to maintain the temperature constant. When the proportioning valve PV-II reaches its fully opened position at point a the control is automatically shifted to the proportioning valve of stove I, namely PV-L From point a on, the automatic control is applied to PV-I and is operative to gradually close PV-I in order to maintain the resultant temperature of stoves I and II constant, at ST. Again, should the resultant temperature between points a and b fall below the predetermined desired temperature ST, the automatic control applied to PV-I will cause a gradual closing of PV-I until the resultant temperature is restored to the desired temperature ST.

The automatic control continues to be applied to PVI until PV-I reaches a fully closed position or a predetermined closed position (point b), and at such time the automatic system is automatically shifted to stove III, the new stove placed into the ON BLAST condition, and will cause the proportioning valve of stove III, namely PV-III, to gradually open between points b and b'. At b' when PV-III reaches its` fully opened position, the control is automatically shifted to the proportioning valve PV- i. This continually repeats itself in the manner shown by FIG. 3. The circuitry which provides for the automatic control in the manner described above will now `be tully discussed.

Referring to FIG. l, it will be noted that there is provided a temperature sensing device l0 in the hot blast main at a point between theblast furnace and the stoves. This temperature sensing device '10 which Vis of a conventional construction, generates an electrical signal which is a function of the actual temperature of the combined blasts leaving the stoves which are in the ON BLAST condition. line 12 to a signal comparator device SC. There is also fed into the signal comparator device SC an electrical signal which is manually set and which is a function of the desired resultant blast temperature, namely, desired set temperature ST, previously discussed in connection with FIG. 2. The signal comparator device SC merely compares the two signals fed therein. Two sets of c0ntacts ARH and ARL respectively, are provided in signal comparator SC and operate as follows. When the actual temperature of the combined blasts, as measured through device l0, is lower than the desired temperature ST, contacts ARL are automatically closed. When, on the other hand, the actual combined blast temperature exceeds the set temperature ST, contacts ARH are automatically closed.

The above therefore indicates the Amanner in which a determination is made as to the relationship between the actual temperature of the combined blasts and the desired temperature ST of the blast. This determination is utilized in controlling the respective proportioning valves of the stoves for the purpose of automatically maintaining the combined blast temperatureas constant as possible and equal to the desired temperature ST.

FIGS. 4 and 5 represent the circuitry which. provides for the fully automatic operation of the staggered system in accordance with the invention.

Table A, below, lists all of the components shown in FIGS. 4 and 5 whichcare associated with stove I, accompanied by a brief description of the manner in which they function.

Such signal is transmitted through Table A Component Description PVO-I Limit switch associated with proportioning valve PV-I 0i stove I and automatically closes when PV-I reaches iully open position.

PVC-I Limit switch associated with proportioning valve PV-l of stove l. and automatically closes when PV-I reaches fully closed position (or predetermined closed position).

IVO R-l Relay having a plurality a-a These are normally of sets of contacts b-b open contacts 'which g actuated thereby, as c-c are closedwhen described in adjacent PVOR-1 1s energized column. but which remain closed for only an adinstable short period of time.

d-d Normally closed contacts, Le., closed when PVO R-I is unenergized and open when PVO R-I is energized.

c-e These are normally j-f open contacts, 1.o.,

g-g closed when PVOR-I is energized and open when PVO R-l is unenergized.

IVC RI Relay having a plurality a-a Normally closed.

of sets of contacts operb-b Normally open. ated thereby, as dec-c scribed in adjacent column.

IRW-I A relay associated with a-a Normally open constove I which is auto* b-b tacts. matically energized when stove I is ON BLAST. This relay and its operation is fully described 1n previously referred to U.S.

Pat. No. 3,034,775. Relay IEW-l actuators a plurality of sets of contacts only two of which are ol pertinence to the present invention; these two sets are described in adjacent column.

HR-I Relay having a single set a-a Normally open.

of contacts actuated thereby, as described in adjacent column.

CSR-I Relay having a pair of rz---a Normally open concontacts actuated b-b tacts. thereby, as described in adjacent column.

CD-A-a relay having a pair of 'sets of normally open contacts, cz-a and b-b. When relay CD-A is unenergized the contacts are open and when the relay 'is energized Vthese contacts are closed.

'CDS-a relay having a pair of sets of normally open contacts, a-a and b-b. When relay CD-B is unenergized the contacts are open, and when the relay is energized `these contacts are closed.

The iirst aspect of the automatic control in accordance with the invention relates to the method and circuitry for selecting the particular .proportioning valve to be regulated at any one time. It has already been demonstrated, particularly with reference to FIG. 3 that at al1 times ,during the operation of the installation only one proportioning valve need be regulated. The circuitry associated with the automatic selection of the particular proportioning valve to be controlled is set forth in FIG. 4.

LI and L2 represents the main power lines for the system. For purposes of easier .reference each horizontal line in FIG. 4 has been identilied by a level number, the uppermost line, for example, being at level 1. In FIG. 4, levels l through 9 represent the circuitry associated with the selection of stove I as the stove whose proportioning valve is to be controlled. Similarly, levels I through 9 represent the circuitry associated with stove II, levels l through 9 represent the circuitry associated with stove III, and levels 1 through 9 represent the circuitry associated with the selection of stove IV.

Referring now particularly to that part of the circuitry in FIG. 4 associated with stove I (levels 1-9), it will be noted that level l has switch PVO-I in series with relay PVOR-I. This means that when switch PVO-I is closed relay IVOR-I becomes energized. This occurs, as previously described, when the proportioning valve of stove I reaches its fully opened position because it is at such point that limit switch PVO-I is automatically closed. It will be noted, however, that normally closed contacts a-a ot relay PVCR-I (level 2) short circuits switch PVO-I (level l) so that relay PVOR-I remains energized though switch PVO-I reopens, so long as relay PVCR-I remains unenergized. Level 3 shows limit PVCI in series with relay PVCR-I. Accordingly, when the proportioning valve PV-I reaches its fully closed position, limit switch PVC-I will be closed, thus energizing relay PVCR-I. It must be noted, however, that normally closed contacts d-d of PVOR-I (level 4) short circuits switch PVC-I so that relay PVCR-I remains energized though switch PVC-I reopens, so long as relay PVOR-I is unenergized.

Thus it is seen that relay PVOR-I and relay PVCR-I are really latching relays and are mutually exclusive. In other words, relay PVOR-I will remain energized so long as relay PVCR-I is unenergized and, similarly, relay PVCR-I remains energized so long as relay PVOR-I is unenergized. In terms of FIG. 3, the latching relays operate so that, for example, stove I will have its relay PVCR energized between point b and point d, and will have its relay PVOR-I energized between points d and f.

Relay CSR-I (level 6 in FIG. 4) is the control selection relay for stove I which, when energized, will be operative to cause stove I to be the stove whose proportioning valve is controlled. In series with relay CSR-I are contacts zz-a of IRW-I. As previously set forth, these contacts a-a will be closed only when stove I is in the ON BLAST condition. Accordingly since relay CSR-I is in series with contacts a-a of IRW-I, stove I can be selected as the one to be controlled only if it is in the ON BLAST condition.

Assuming now that the stoves are in the condition just preceding point a in FIG. 3, at which time stoves I and II are the only ones in the ON BLAST condition. At such point, proportioning valve PV-I is fully open and relay PVOR-I is energized. Such will cause `contacts e-e of relay PVOR-I (level 6) to be closed. At such time, however, none of the other three stoves have their PVOR relays energized, and thus there is no complete circuit through level 6 in FIG. 4. Stove II, however, is slowly approaching point a and when it does reach point a its proportioning valve PV-II will be fully opened and relay PVOR-II (level 1') will become energized. The energization of relay PVOR-II will cause contacts c-c thereof (level to close, thus completing the circuit between lines L1 and L2, thereby energizing relay CSR-J, causing the control to shift to such stove I. The completion of this circuit also energizes holding relay HR-I,

whereby contacts a-zz thereof (level 8) are closed. Such Vshift to another stove,

closing on contacts a-a of holding relay HR-I will insure the continued energization of relay `CSR-I though contacts c-c of relay PVOR-II (level 5) will reopen as these are contacts which remain closed for only a short period of time, as previously explained.

Thus it is seen that at point a', which is the point where the proportioning valve of stove II reaches its fully open position, control selection relay CSR-I is automatically energized whereby the control is automatically shifted to stove I, as required. The control will remain with stove I so long as control selection relay CSR-I remains energized, and the same will remain energized until contacts a-a of relay IRW-I reopen, such happening automatically when point b in FIG. 3 is reached, which is when stove I leaves the ON BLAST condition. Another way of stating the function of the circuitry just described is that: when any stove that is ON BLAST has its PVOR-I relay energized, such stove will automatically be selected as the stove to be controlled the moment any one of the other stoves has its PVOR relay energized, i.e., the moment that any one of the other stoves has its proportioning valve reach the fully open position. This circuitry therefore takes care of the automatic shifting at points a', b', c', d', e', etc., since all the stoves, as seen in FIG. 4, have circuitry associated therewith identical to that discussed in connection with stove I (levels l through 9).

The other type of condition at which it is necessary to change the automatic control from one stove to another is that which is illustrated, insofar as stove I is concerned, at point d in FIG. 3. In this connection it will be recalled that between points b and a" relay PVCR-I was energized. During this interval therefore, between b and d', contacts b-b of PVCR-I (level 9) are closed. This in itself does not complete a circuit from LI to L2, through relay CSR-I, unless contacts a-a of IRW-I (level 6) are also closed, and these contacts will only close when stove I goes into the ON BLAST condition, which is at point d. Accordingly, it is seen that when stove I has its proportioning valve fully closed such proportioning valve would automatically become the one to be controlled when stove I goes into the ON BLAST condition, as it does at point a'. The control will remain with stove I beginning at point d until the proportioning valve PV-I of stove I reaches the fully opened position at point d', since at such point limit switch PVO-I will close causing relay PVOR-I to become energized, thus automatically de-energizing relay PVCR-I, and opening contacts b-b thereof at level 9. This is exactly what is desired because it is at point d that it becomes necessary for the control to automatically and it will be stove IV which is the one whose control selection relay CSR-IV will be energized.

Since all the stoves are provided with identical circuitry, such circuitry will provide for the automatic shifting of control to the correct stove at points b, c, d, e, f, etc.

From the above it is seen that the circuitry of FIG. 4 is such as to automatically select the correct proportioning valve to be controlled exactly in the manner set forth in FIG. 3.

With reference to FIG. 5, there will now be described the circuitry associated with the determination of the manner in which the particular proportioning valve to be controlled is in fact controlled so as to maintain the resultant temperature of the two stoves which are ON BLAST equal to the predetermined desired temperature ST.

In this connection reference is briey made to FIG. 3 where it is noted that the operation of the system falls into two categories identified in FIG. 3 by A and B. In a category A condition, the stove which is controlled is the fresher of the two stoves which are ON BLAST, as between points a and a', b and b', c and c', etc. In a category B condition the stove which is controlled is the cooler of the two stoves which are ON BLAST, as between points a and b, b and c, c and d, etc. Under category A condition, should the actual combined blast s, 178,1 eo

temperature be less than the set temperature ST, will lbe necessary to increase the opening of the proportioning Vtemperature be less than the set temperature ST it would be necessary to decrease the opening of the proportioning valve which is being controlled in order to maintain the resultant temperature at ST. Accordingly, while the particular proportioning valve to be controlled is determined by the circuitry in FIG. 4, it is necessary to make a further determination as to whether the stove whose proportioning valve is being controlled is operating in a category A or a category B condition.

In FIG. 5 the circuitry in levels 1 through 5 determines whether the system is operating in a category A condition,

and the circuitry between levels 6 and 13 is for the pur` pose of determining whether the system is operating .in a category B condition. By reference to FIG. 3 it will be noted that whenever the system is'operating in category A condition one of the stoves ON BLAST has its PVOR relay energized while the other stove which is ON BLAST has its PVCR relay energized. For example, between points a and a', stove I has its PVOR relay energized and stove Il has its PVCR relay energized. The circuitry in levels 1 through 5 is such that relay CD-A (control directional relay for category A condition) will be energized whenever one of the stoves has its PVOR relay energized and any other stove which is ON BLAST has its PVCR relay energized. It will be apparent from an examination of levels 1 through 5 that the circuit show-n therein provides for all possible combinations of two stoves meeting the requirements for category A condition. Accordingly, control directional-relay CD-A will automatically be energized when the system is operating in a category A condition.

Referring again to FIG. 3, it will be noted lthat whenever the system is operating in a category B condition, the

two stoves which are ON BLAST have their PVOR relays energized. The converse is also true, namely, that whenever any two stoves have ytheir PVOR relays energized the system is operating in a category B condition. In FlG. 5, the circuitry between levels 6 and 13 is such that relay CD-B V(control directional relay for category B condition) is automatically energized whenever any two stoves have their PVOR relays energized. An examination of levels 6 through 13 indicates that any combination of two stoves having their PVOR relays energized will automatically cause the energization of relay CD-B.

Levels 14 through 25 in FIG. 5 indicate the manner in which the proportioning valves of the respective stoves are actually controlled by their respective control drives VCD (previously described in connection with FIG. 1), Iin order to maintain the temperature of the combined blast at its desired temperature ST.

It will be recalled that contact ARL in signal comparator device SC is closed when the actual combined temperature of the blast is less than the desired temperature ST. Assuming that we are operating in category A condition, and between points aand a in FIG. 3, and that the combined temperature is less than the desired temperature ST. In such event: Contacts ARL (level 15) will be closed; and, since we are operating under category A, relay CD-A is energized and contacts a-a thereof (level 14) are closed.

Since stove Il is the one which has been selected by the circuitry of FIG. 4, and selector relay SR-II will be energized, contacts a-a thereof (level Ztl) will be closed, thereby completing a circuit to terminal o of valve control drive VCD-II of stove II and such will cause the increased opening of the proportioning valve PV-II.

If for example, while still operating between points a and a (FIG. 3) the combined temperature becomes greater than the set temperature ST, contacts ARH (level 19) will be closed. Also, since we are operating in a l2 category A condition relay CD-A is energized and contacts b-b thereof (level 1S) are closed. A circuit is now completed to terminal c of control drive VCD-II through closed contact b-b of CSR-II (level 21), causing the proportioning valve PV-II to close.

In this manner it is seen rthat the control drive VCD-II Vautomatically opens .or closes the proportioning valve PV- -II to maintain at all times the combined temperature of the yblast equal to the desired temperature ST.

Assuming now that we are operating under category B condition and, for example, between points a and b in FIG. 3, and that the combined temperature is less than the desired temperature ST.Y In such event contacts ARL (level 15), vwill be closed and, since we are operating under category B, relay CD-.B is energized and contacts a-a thereof (level 16) are closed.

Since under the conditions set forth above, stove I is the one which has been selected for control by the circuitry of FIG, 4, and selector relay SR-I will be energized, contacts b-b thereof (level 18) will be closed, :thereby completing a circuit to terminal c of valve control drive VCDI .of stove I, and such will cause proportioning valve PV-I to move in a closing direction.

If now, while still operating between points a' and b (PEG. 3) the combined temperature becomes greater than the set temperature ST, contacts ARH (level 19) will be closed. Also, since we are operating in category B condition relay CD-B is energized and contacts b-b thereof (level 20) are closed. A circuit is now completed to terminal o of control drive VCD-I through closed contacts -a-a of CSR-I (level 1X6), causinf7 the proportioning Valve PV-I to move in an openin g direction.

It is thus seen that the control drive of CD-I automatically opens or closes the proportioning valve PV-I to :maintain at all times the combined temperature of the blast at the desired temperature ST.

As described above it is'seen that the present invention provides a systemwherein a plurality of stoves are placed in theON BLAST condition in staggered relation and vwherein there is provided means for automatically maintaining the temperature of the combined -blast at a predetermined desired temperature. In accordance with the invention, it has been demonstrated that the automatic control system has been arranged so that only one stove at any one time need be controlled and the circuitry of FIG. 4 sets forth the manner in which the particular stove to be controlled at any one time is selected. The circuitry of FIG. 5 shows the manner in which the particular stove which has been'selected has its proportioning valve controlled so that 'the latter is caused to be actuated in order to maintain the temperature of the combined blasts at a predetermined value.

Referring now to FIG. 6 vthere is shown a modification of the 4p-referred'embodiment of the invention. The arrangement shown in FIG. 6 is in all respects identical to that shown in FIG. l except only for the addition of a cold bla-st bypass which permits some of the cold -blast to bypass the stove and to be introduced into mixer M Where lit is thoroughly combined with the resultant hot blastfrom the stoves, prior to entering the blast furnace. A mixed blast buttery valve MBBVis provided in the cold blast bypass in order to control the 4amount of cold blast which is bypassed. When the buttery valve MBBV is Vfully closed, the system operates exactly in the manner described above in conjunction with FIGS. l to 5. The cold Iblast bypass is utilized as a line tempering control of the blast temperature for the blast furnace. More specifically,

'it may `be that with the normal operation of the system described in FIG. l, the hunting eifect produces iluctuations in the resulting temperature beyond a predetermined permissible amount. If such is desired to be eliminated, the set temperature ST can be selected to be slightly higher than the actual desired temperature, with the ne control being obtained by mixing a slight amount of bypassed cold air with the resultant exiting hot blast from the stoves. Toward this end, a thermosensitive device 14 is placed inside the blast furnace and generates an electrical signal to comparator device 16. Said comparator device 16 compares the signal from thermosensitive element 14 with a signal proportional to the desired temperature and transmits the differential signal to control drive 13 for valve MBBV. Thus it is seen that the use of a cold blast bypass in the manner shown in FIG. 6 can be used for line control of the temperature of the blast entering the blast furnace.

It should be noted that the cold blast bypass is an auxiliary additional feature which is not usually necessary as the automatic control system described in FIGS. 1 through 5 provides results well within the permissible tolerance.

The use of the bypass feature in FIG. 6 also gives the installation greater flexibility as it permits the system to operate, if desired, with only one stove being ON BLAST at any one time, in which case the cold blast bypass provides the adjustable amount of cold blast to be mixed with the hot blast in order to maintain a predetermined desired resultant temperature.

Also of importance with respect to the embodiment in FG. 6 is the fact that the use of the cold blast bypass enables resultant temperatures of blast to be obtained which are lower than the temperature of the exiting hot blast whether the installation is operating with one or two stoves in the ON BLAST condition at any one time.

While we have shown and described the preferred embodiments of our invention, it will be understood that the invention may be embodied otherwise than as herein specically illustrated or described, and that in the illustrated embodiments certain changes in the details of construction and in the form and arrangement of parts may be made without departing from the underlying idea or principles of this invention within the scope of the appended claims.

Having thus described our invention, what we claim and desire to secure by Letters Patent, is:

l. In a blast furnace installation having a multi-stove system for supplying a continuous relatively constant volume of hot blast to a blast furnace, means for supplying cold air blast in parallel relation to the stoves of said system, means for sequentially placing said stoves in the ON BLAST condition in staggered relation with a new stove being placed ON BLAST while another stove is still in the ON BLAST condition but at a temperature below that of said new stove, whereby two stoves are ON BLAST at all times, means for combining the hot blast outputs of said new and said other stove to provide a resultant hot blast, means for automatically maintaining the resultant blast exiting from said two stoves at a substantially constant predetermined temperature, proportioning valve means for each stove for regulating the admission of said cold air blast therethrough from said supplying means, said automatic maintaining means comprising means for maintaining the proportioning valve of one of said two stoves fully opened and means for controlling the extent of opening of the proportioning valve of the other of said two stoves so that the temperature of said resultant blast exiting said two stoves is substantially equal to said predetermined temperature, whereby only one of the two stoves which are ON BLAST is required to be controlled.

2. In a blast furnace installation having a multi-stove system for supplying a continuous relatively constant volume of hot blast to a blast furnace, means for supplying cold air blast in parallel relation to the stoves of said system, means for sequentially placing said stoves in the ON BLAST condition in staggered relation with a new stove being placed ON BLAST while another stove is still in the ON BLAST condition but at a temperature below that of said new stove, whereby two stoves are ON BLAST at all times, means for combining the hot blast outputs of said new and said other stove to provide .other stove which is then ON BLAST for rnaintaininU `a resultant hot blast, valve means for each stove for regulating the admission of said cold air blast therethrough from said supplying means, electrically operated drive means operatively connected to each of said valve means, means for generating an electrical signal comparative of the actual temperature of said resultant blast entering the blast furnace with `a predetermined temperature, means operatively connected to the drive means for the valve means of one of said two stoves for maintaining said latter valve means fully open, and means for automatically transmitting said electrical signal to the electrically operated drive means of the other of said two stoves whereby the extent of opening of the valve means ,of the other stove is automatically controlled in response to said electrical signal so that `the temperature of the resultant blast exiting from said two stoves is substantially Vthat oi' said predetermined temperature.

3. ln a blast furnace installation having a multi-stove system for supplying a continuous relatively constant volume of hot blast to a blast furnace, means for supplying cold air blast in parallel `relation to the stoves of said system, means for sequentially placing said stoves in the ON BLAST condition in staggered relation with a new .stove being placed ON BLAST while another stove is still in the ON BLAST condition but at a temperature below that of said new stove, whereby two stoves are ON BLAST at all times, means for combining the hot blast outputs of said new and said other stove to provide a resultant hot blast, valve means for each stove for regulating the admission of said cold air blast therethrough from said supplying means, electrically operated drive means operatively connected to each of said valve means, means for generating an electrical signal comparative of the actual temperature of said resultant blast entering the blast furnace with a predetermined temperature, circuit means for automatically transmitting said electrical signal to the electrically operated drive means of a fresh stove at the moment that the latter is placed in the ON BLAST condition, and means operatively connected to the drive means for the valve means of the at such moment, said latter valve means fully opened,

such fresh stove having its valve means controlled in response to the electrical signal, so that the resultant temperature of the resultant blast exiting the two stoves Awhich are ON BLAST is substantially that of said predetermined temperature, whereby said predetermined temperature is substantially maintained with only one of the stoves which is ON BLAST being controlled in response to said electrical signal.

4. ln a blast furnace installation having a multi-stove `system for supplying a continuous relatively constant yvolume of hot blast to a blast furnace, means for supplying cold air blast in parallel relation to the stoves of said system, means for sequentially placing said stoves in the ON BLAST condition in staggered relation with a new Vstove being placed ON BLAST while another stove is .still in the ON BLAST condition but at a temperature below that of said new stove, whereby two stoves are ON BLAST at all times, means for combining the hot blast outputs of said new and said other stove to provide a resultant hot blast, valve means for each stove for regulating the admission of said cold air blast therethrough from said supplying means, electrically operated drive means operatively connected to each of said valve means, means for generating an electrical signal comparative of the actual temperature of said resultant blast entering the blast furnace with a predetermined temperature, circuit means fol automatically transmitting said electrical signal to the electrically operated drive means of a fresh stove at the moment that the latter is placed in the ON BLAST condition, and means operatively connected to the drive means for the valve means of the other stove which is then ON BLAST for maintaining, at such moment, said latter valve means fully opened,

`such fresh stove having its valve means controlled in response to the electrical signal so that the resultant temperature of the blast exiting the two stoves which are ON BLAST is substantially that of said predetermined temperature, land means for automatically shifting said electrical signal to the drive means of said other stove when the valve means of said fresh stove reaches a predetermined open position thereof which is maintained thereby after said shifting, whereby the resultant blast entering the furnace is maintained at substantially said predetermined temperature at all times, with only `one of the stoves which is ON BLAST being controlled in respouse to said electrical signal.

5. In a blast furnace installation having a multi-stove system for supplying a continuous relatively constant volume of hot blast to a blast furnace, means for supplying cold air blast in parallel relation to the stoves of said system, means for sequentially placing said stoves inthe ON BLAST condition in staggered relation vwith a new stove being placed ON BLAST while another stove is still in the ON BLAST condition but at a temperature below that of said new stove, whereby two stoves are ON BLAST at all times, means for combining the hot blast outputs of said new and said other stove to provide a resultant `hot blast, Valve means for each stove for regulating the admission of said cold air blast` therethrough from said supplying means, drive means operatively connected to each of said valve means, means for generating an electrical signal comparative of the actual temperature of the resultant blast ventering the blast furnace with a predetermined temperature, means operatively lconnected to the driveV means for the lvalve means of one of said two stoves for maintaining said latter valve means fully open, and means vfor automatically transmitting said electrical signal to the drive means of the other of said two stoves whereby the extent of opening `of the valve means of the other stove is automatically controlled in kresponse to said electrical signal so that the temperature of the resulting blast exiting from said twostoves is substantially that of said predeterminedtemperature.

6. In a blast furnace installation having a multilstove system for supplying a continuous relatively constant volume of hot blast to a blast furnace, means for supplying cold air blast in parallel relation to the stoves of said system, means for sequentially placing said stoves in the ON BLAST condition in staggered relation with a new stove being placed ON BLAST while anotherstove is still in the ON BLAST condition but atta temperature below that of said new stove, whereby two stoves are ON BLAST at all times, means for combining the hot blast outputs of said new and said other stove to provide a resultant hot blast, valve means for each stove for regulating the admission kof said 4cold air blast therethrough from said supplying means, drive means operatively connected to each of said valve means, means for `generating an electrical signal comparative of the actual temperature of the resultant blast entering the blast furnace with a predetermined temperature, circuit means for automatically transmitting said electrical signal to the drive means of a fresh stove at the moment the latter is .t f3 placed in the ON BLAST condition, and means operatively connected to the drive means for the valve means of the other stove which is then ON BLAST for maintaining, at such moment, said latter valve means fully opened,

such fresh stove having its valve means in response to the electrical signal, so that the resultant temperature of the resultant blast exiting the two stoves which are ON BLAST is substantially that of said predetermined temperature, whereby said predetermined temperature is substantially maintained with only one of the stoves which is ON BLAST being controlled in response to said electrical signal.

7. In a blast furnace installation having a multi-stove system for supplying a continuous relatively constant volume of hot blast to a blast furnace, means for supplying cold air blast in parallel relation to the stoves of said system, means for sequentially placing said stoves in the ON BLAST condition in staggered relation with a new stove being placed ON BLAST while another stove is still in the ON BLAST condition but at a temperature below rthat of said new stove, whereby two stoves are ON BLAST at all times, means for combining the hot blast outputs of said new and saidother stove to provide a resultant hot blast, valve means foreach vstove for regulating the admission of said cold air blast therethrough from said supplying means, drive means operatively connected to each of said valve means, means for generating an electrical signal comparative of the actual -temperature of the resultant blast entering the blast furnace with a predetermined temperature, circuit means for automatically transmitting said electrical signal to the drive ymeans* of 'a freshstove at Vthe moment that the latter is placed in the ON BLAST condition, means operatively connected to the drive means for the valve means of the other stove which is then ON BLAST for maintaining, at such moment, said latter valve means fully opened, such fresh stove having its valve means controlled in response to the electrical signal so that the resultant temperature of the blast exiting the two stoves which are ON BLAST is substantially that of said predetermined temperature, and means for automatically shifting said electrical signal tothe Vdrive means yof said other stove when the valve means of lsaid fresh stove `reaches a predetermined open position thereof which is maintained thereby after said shifting, whereby the resultant 'blast entering the vfurnace is maintained at substantially said predetermined temperature at all times, with onlyone of the stoves which is ON BLAST being vcontrolled in respouse to said electrical signal.

References Cited bythe Examiner UNITED STATES PATENTS 1,941,446 12/33 Isley 263-19 3,034,775 5/62 Jansen et al. 263-19 3,153,532 10/64 Touzalin 26S- 19 CHARLES SUKALO, -Prmary Examiner.

JOHN I. YCAMBY, Examiner. 

1. IN A BLAST FURNACE INSTALLATION HAVING A MULTI-STOVE SYSTEM FOR SUPPLYING A CONTINUOUS RELATIVELY CONSTANT VOLUME OF HOT BLAST TO A BLAST FURNACE, MEANS FOR SUPPLYING COLD AIR BLAST IN PARALLEL RELATION TO THE STOVES OF SAID SYSTEM, MEANS FOR SEQUENTIALLY PLACING SAID STOVES IN THE "ON BLAST" CONDITION IN STAGGERED RELATION WITH A NEW STOVE BEING PLACED "ON BLAST" WHILE ANOTHER STOVE IS STILL IN THE "ON BLAST" CONDITION BUT AT A TEMPERATURE BELOW THAT OF SAID NEW STOVE, WHEREBY TWO STOVES ARE "ON BLAST" AT ALL TIMES, MEANS FOR COMBINING THE HOT BLAST OUTPUTS OF SAID NEW AND SAID OTHER STOVE TO PROVIDE A RESULTANT HOT BLAST, MEANS FOR AUTOMATICALLY MAINTAINING THE RESULTANT BLAST EXITING FROM SAID TWO STOVES AT A SUBSTANTIALLY CONSTANT PREDETERMINED TEMPERATURE, PROPORTIONING VALVE MEANS FOR EACH STOVE FOR REGULATING THE ADMISSION OF SAID COLD AIR BLAST THERETHROUGH FROM SAID SUPPLYING MEANS, SAID AUTOMATIC MAINTAINING MEANS COMPRISING MEANS FOR MAINTAINING THE PROPORTIONING VALVE OF ONE OF SAID TWO STOVES FULLY OPENED AND MEANS FOR CONTROLLING THE EXTENT OF OPENING OF THE PROPORTIONING VALVE OF THE OTHER OF SAID TWO STOVES SO THAT THE TEMPERATURE OF SAID RESULTANT BLAST EXITING SAID TWO STOVES IS SUBSTANTIALLY EQUAL TO SAID PREDETERMINED TEMPERATURE, WHEREBY ONLY ONE OF THE TWO STOVES WHICH ARE "ON BLAST" IS REQUIRED TO BE CONTROLLED. 